1. Field of the Invention
The invention relates to a reduction vessel for the reduction of metal-oxide-bearing material, particularly of iron ore, by means of a reduction gas flowing countercurrently to the metal-oxide-bearing material, which reduction vessel is provided with an inlet for the metal-oxide-bearing material, an inlet for the reduction gas, an outlet for off-gas and an outlet for reduced material, downstream of which outlet a lower sealing leg is connected, a supply line for a first sealing gas being provided at the lower sealing leg in order to seal the reduction vessel against the environment. The invention further relates to a process for sealing a reduction vessel for the reduction of metal-oxide-bearing material, particularly of iron ore.
2. Description of the Related Art
Arrangements for sealing a reduction vessel against the environment are known (Direct from Midrex, Vol. 14, No. 3, 3rd quarter of 1989).
According to DE-A-34 32 090, sulfur-bearing ore is reduced in a shaft furnace in counterflow with reduction gas. The off-gas exiting the furnace is divided into two flows, the first flow being used for preheating and desulfurization of the ore which is located in a ore bin above the shaft furnace and the second flow being fed to a catalytic gas converter together with hydrocarbons in order to generate reduction gas.
Above the ore bin of the arrangement described in DE-A-34 32 090, a container is located from which ore is charged into the ore bin. Inert gas is injected into the connection between this container and the ore bin in order to prevent sulfur-bearing off-gas from exiting the ore bin through this connection. This measure thus serves to establish a gas seal.
An arrangement for cooling a gas-permeable bed of subsiding solid particles, for example, of reduced ore pellets, at the outlet of a reduction shaft furnace is known from AT-B-328 481.
Arrangements of this type are also known from DE-C-26 51 309 and U.S. Pat. No. 4,046,557. In these known arrangements, partly off-gas (waste reduction gas) from the reduction shaft furnace is used for cooling. These documents do not give any statements about the sealing of the reduction shaft furnace against the environment in order to prevent the gas contained in the reduction shaft furnace from exiting.
U.S. Pat. No. 4,212,452 describes a plant in which iron oxide is reduced to sponge iron in a shaft furnace through the addition of solid carbon-bearing material, which is gasified in an upper zone of the shaft furnace, and through the addition of reduction gas containing CO and H.sub.2 in a central zone of the shaft furnace. The iron oxide, together with the solid carbon-bearing material, is charged from the top into the shaft furnace and flows through the shaft furnace from the top to the bottom, partly cocurrently and partly countercurrently to the reduction gases. In a lower zone of the shaft furnace, the sponge iron formed by reduction is cooled with cool, dry reduction gas. The shaft furnace is sealed towards the top and bottom with one CO.sub.2 -operated gas seal each in order to prevent the undesirable escape of reduction gas from the shaft furnace, CO.sub.2 being recovered therein from waste reduction gas through gas scrubbing. This known arrangement has the disadvantage that the sealing gas, CO.sub.2, may enter the shaft furnace, which is undesirable with regard to reduction.
An arrangement which is used, for example, for the direct reduction of iron-oxide-bearing material by means of reduction gas in a shaft furnace is known from U.S. Pat. No. 3,850,616. The iron-oxide-bearing material flows through the shaft furnace from the top to the bottom countercurrently to the reduction gas and is cooled with cool reduction gas in the lower zone of the shaft furnace. In order to prevent reduction gas from exiting the shaft furnace, a gas seal operated with inert gas is provided at the lower end of the shaft furnace. This known arrangement has the disadvantage of high consumption of expensive inert gas.
Processes in which iron-oxide-bearing material is reduced in a shaft furnace by means of reduction gas and melted in a melting unit which is structurally connected with the shaft furnace are known from U.S. Pat. No. 4,248,626 and U.S. Pat. No. 4,270,740. In the melting unit, reduction gas is generated by coal gasification.
The reduction gas is withdrawn from the melting unit and cooled before it is charged into the shaft furnace in order to prevent the material reduced in the shaft furnace from agglomerating. In order to prevent the very hot reduction gas from being carried over from the melting unit directly into the shaft furnace, a gas seal is provided in the direct connection between the melting unit and the shaft furnace.
The applicant knows that gas seals operated with nitrogen, which seal shaft furnaces against the environment, are customary. Gas seals of this type have the disadvantage that the generation of nitrogen involves high technical expenditure, which results in high costs because large amounts of nitrogen are consumed.